The UK, The Netherlands, Scandinavia
and parts of Germany experienced a series of unusually bright and intensely
colourful sunset and dawn twilights over the last few days. They
are sometimes caused by volcanic
dust ejected into the stratosphere but this
is unlikely to be the reason for the recent ones.
Europe's cold anticyclonic weather could also have caused a build up of tropospheric
haze and aerosol with clear air above that enhanced the twilight.

Another and more likely explanation is the presence of very high (15-25 km) and
thin 'Type1' polar stratospheric clouds, PSCs.
The exceptionally low temperatures needed to form them
have existed over the area of Europe where the twilights have been sighted for
the last few days.Type1 PSCs
composed of nitric acid compounds are less colourful and bright than the better
known Type2 or nacreous
clouds made of ice crystals but here they have scattered high altitude sunlight
to give us some truly memorable twilight skies.